Lingyun Sun

Dielectric properties of Y and Nb co-doped TiO 2 ceramics

In this work, the (Y0.5Nb0.5)xTi1−xO2 (xu2009=u20090.001, 0.01, 0.02, 0.04, 0.06 and 0.1) ceramics (as called YNTO) were fabricated by synthesized through a standard solid-state reaction. As revealed by the X-ray diffraction (XRD) spectra, the YNTOs exhibit tetragonal rutile structure. Meanwhile, the grain size of YNTO ceramics increased and then decreased with the increase of x value, and the largest value reached when xu2009=u20090.02. All the YNTO samples display colossal permittivity (~102–105) over a wide temperature and frequency range. Moreover, the optimal ceramic, (Y0.5Nb0.5)0.02Ti0.98O2, exhibits high performance over a broad temperature range from 20u2009°C to 180u2009°C; specifically, at 1u2009kHz, the dielectric constant and dielectric loss are 6.55u2009×u2009104 and 0.22 at room temperature, and they are 1.03u2009×u2009105 and 0.11 at 180u2009°C, respectively.

Calcining temperature dependence on structure and dielectric properties of CaCu3Ti4O12 ceramics

CaCu3Ti4O12 powders were obtained by calcining the precursor, which was synthesized by sol–gel process, at different temperatures, and the ceramics were obtained by dry pressing and sintering using the powders. The dependence of calcining temperature on the microstructure and dielectric properties of the ceramics was studied. The results show that the grain size of the powder grows larger with increasing calcining temperature from 700 to 1000xa0°C. With increasing the calcining temperature, the grain size of CCTO ceramics increases and then decreases, while the porosity exhibits an opposite trend. The ceramic, obtained by using the powders calcined at 850xa0°C, shows the largest grain size, and it also shows good dielectric properties with the dielectric constant of 2.61xa0×xa0104 and the dielectric loss of 0.12 at 1xa0kHz.

Electrochemical properties of NiCoO2 synthesized by hydrothermal method

NiCoO2 microspheres were successfully synthesized via an easy hydrothermal method, followed by an annealing process at 350 °C under a nitrogen atmosphere. The X-ray diffraction results show that a single phase NiCoO2 was synthesized. The results of electrochemical measurements show that the NiCoO2 exhibits a high specific capacitance of 760 and 470 F g−1 at current densities of 1 and 16 A g−1, respectively, and the specific capacitance retention is 40.9% after 5000 cycles at the current density of 16 A g−1. This reveals the great potential of NiCoO2 as an electrode material for high-performance supercapacitors.

Hydrothermal process fabrication of NiO–NiCoO2–Co3O4 composites used as supercapacitor materials

A composite consisting of Co3O4, NiCoO2 and NiO is prepared by a simple and easy hydrothermal method followed by calcining at 300u2009°C. The composition, morphology and microstructure of NiO–NiCoO2–Co3O4 composites are examined by X-ray diffraction, field emission scanning electron microscope and transmission electron microscopic. The electrochemical performances of NiO–NiCoO2–Co3O4 composites are characterized by cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy in 3xa0M KOH electrolyte. The results of electrochemical measurements show that the NiO–NiCoO2–Co3O4 composites exhibit a high specific capacitance of 990 and 580xa0F/g at the current densities of 1.0 and 10xa0A/g, respectively. About 50% of the maximum specific capacitance can still be retained after 1000 continuous CD cycles at 10xa0A/g. It reveals a great potential of NiO–NiCoO2–Co3O4 composites used in high-performance energy-storage systems.

Hydrothermal Synthesized of CoMoO 4 Microspheres as Excellent Electrode Material for Supercapacitor

The single-phase CoMoO4 was prepared via a facile hydrothermal method coupled with calcination treatment at 400xa0°C. The structures, morphologies, and electrochemical properties of samples with different hydrothermal reaction times were investigated. The microsphere structure, which consisted of nanoflakes, was observed in samples. The specific capacitances at 1xa0Axa0g−1 are 151, 182, 243, 384, and 186xa0Fxa0g−1 for samples with the hydrothermal times of 1, 4, 8, 12, and 24xa0h, respectively. In addition, the sample with the hydrothermal time of 12xa0h shows a good rate capability, and there is 45% retention of initial capacitance when the current density increases from 1 to 8xa0Axa0g−1. The high retain capacitances of samples show the fine long-cycle stability after 1000 charge-discharge cycles at current density of 8xa0Axa0g−1. The results indicate that CoMoO4 samples could be a choice of excellent electrode materials for supercapacitor.

Improved dielectric properties in CaCu 3 Ti 4 O 12 ceramics modified by TiO 2

The fabrication of TiO2 modified CaCu3Ti4O12 (wu2009=u20090, 0.01, 0.1, 2%) ceramics were obtained by a sol–gel process. The influence of TiO2 amount on the microstructures and dielectric properties was studied. The results indicate that TiO2 modified CaCu3Ti4O12 ceramics exhibits higher density, more obvious grain boundaries, and larger grains, and show improved dielectric properties, including colossal permittivity (~u2009104) and comparably low dielectric loss (~u20090.1–2.3) at room temperature over the frequency range from 100xa0Hz to 1xa0MHz. The colossal permittivity could be explained by an internal boundary layer capacitance effect. CaCu3Ti4O12 modified with wu2009=u20090.01% TiO2 shows improved dielectric constant (~u20096.81u2009×u2009104) and low dielectric loss (~u20090.12) at room temperature and 1xa0kHz, and it also exhibits good performance over a broad temperature from 20 to 200xa0°C. The results show that TiO2 modification can make an improvement in both microstructures and dielectric properties for CaCu3Ti4O12.

A facile hot plate annealing at low temperature of Pb(Zr 0.52 Ti 0.48 )O 3 thin films by sol–gel method and their ferroelectric properties

Perovskite-structure Pb(Zr0.52Ti0.48)O3 ferroelectric thin films were fabricated on fluorine doped tin oxide substrate by sol–gel method and then followed by a facile hot plate annealing at low temperature of 550xa0°C. With the increase of the annealing residence time from 2 to 40xa0min, phase transformation from pyrochlore to pure perovskite occurred. The obtained films exhibited excellent transmittance in the range of the visible light. With the annealing residence time became longer, the optical band-gap of the thin films became wider. Dielectric permittivity and remnant polarization value increased with the incremental annealing residence time to 40xa0min and then decreased for the sample annealded for 60xa0min. The highest dielectric permittivity and remnant polarization were observed for the thin films annealed at 550xa0°C for 40xa0min. The values of remnant polarization and coercive field for PZT film annealed for 40xa0min were 40.3xa0µC/cm2 and 228xa0kV/cm, respectively.

Oxygen vacancy induced bismuth basic nitrate with excellent photocatalytic activity

A novel gray bismuth basic nitrate photocatalyst was synthesized. The results of Raman scattering spectroscopy, X-ray photoelectron spectroscopy and photoluminescence spectroscopy supported the presence of oxygen vacancies. Gray bismuth basic nitrate exhibits higher activity than white bismuth basic nitrate and BiOCl which is one of the most extensively studied bismuth-based photocatalytic material. The oxygen vacancies and internal electric field in bismuth basic nitrate possibly make it one of the promising materials for the degradation of environmental pollution.